You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
You are given a passage. Using the information present in the passage, you need to classify it into one of the 10 topics: 0 - 'Society & Culture', 1 - 'Science & Mathematics', 2 - 'Health', 3 - 'Education & Reference', 4 - 'Computers & Internet', 5 - 'Sports', 6 - 'Business & Finance', 7 - 'Entertainment & Music', 8 - 'Family & Relationships', 9 - 'Politics & Government'.

	Optical mice use an LED and a camera to rapidly
capture images of the surface beneath the mouse.
The infomation from the camera is analyzed by a
DSP (Digital Signal Processor) and used to detect
imperfections in the underlying surface and
determine motion. Some materials, such as glass,
mirrors or other very shiny, uniform surfaces
interfere with the ability of the DSP to
accurately analyze the surface beneath the mouse.
\nSince glass is transparent and very uniform, the
mouse is unable to pick up enough imperfections in
the underlying surface to determine motion.
Mirrored surfaces are also a problem, since they
constantly reflect back the same image, causing
the DSP not to recognize motion properly. When the
system is unable to see surface changes associated
with movement, the mouse will not work properly.
Solution: 4
Why? The passage talks about optical mice or mouse throughout which is a part of computer system. Thus, it is correctly classified to "Computers & Internet" 

New input: unless the cracking is painful, it is not unusual or dangerous for your knees to "crack".\n\nLunges are excellent for strengthening the muscles around the knee joint. Make sure that you are not leaning over the knee, that the knee is right above the foot during the lunge and that you maintain a straight upright movement.\n\nDo not do hamstring excercises that will pull on the knee joint if you have problems with your knee. \n\nelipticals are good for running on with minimal knee and ankle stress. \n\nyou can also get large elastic bands...stand in them, and step out to the side pulling on the bands, then back in. Don't pull harder than is comfortable, this will help increase the stablization of the knee.\n\nLaying on your back you can pull your knee to your chest, and then extend it, locking your knee holding the leg just over the ground..repeating, this will also help strengthen the muscles around the knee with minimal weight on it.\n\nAlways is good to speak with a doctor or physical therapist if you have concerns.
Solution:
2